#define _CRT_SECURE_NO_WARNINGS 1
#include<assert.h>
#include<stdio.h>
char* my_strstr(char const* str1, char const* str2) {
	assert(str1 && str2);
	char * b =(char*) str1;
	if (!*str2)return (char*)str1;
	while (*b) {
		char * s1 = b, * s2 =(char*) str2;
		while (*s1 == *s2 && *s1++ && *s2++);
		if(!*s2)
		return b;
		b++;
	}
	return NULL;
}
int main() {
	printf("%s", my_strstr("abcd", "bc"));
	return 0;
}